Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Nafion through

FIGURE 4.5 Nafion through-plane resistance as a function of current density at three fuel cell operating temperatures 100% RH for both the anode and the cathode 3.0 atm backpressure with hydrogen and air feeding Nafion - 12-based baseline MEA with an active area of 4.4 cm [3]. (For color version of this figure, the reader is referred to the online version of this book.)... [Pg.140]

Therefore, one main drawback of the PEMFC configuration with a standard proton exchange membrane (such as Nafion) and a standard platinum gas diffusion cathode is the cathode depolarization caused by a mixed potential resulting from the methanol crossover through the mem-... [Pg.95]

The usual working temperature of fuel cells with Nafion-type membranes is 80 to 90°C. Under these conditions, moisture must be supplied to keep the membranes wet, which usually is attained by passing the reactant gases through water that is somewhat warmer (by 5 to 10°C) than the cell s working temperature, thus saturating them with water vapor. [Pg.364]

Photocatalytic oxidation of ethanol on Pt/ri02 and Nafion coated Ti02 catalysts were studied using in situ infrared IR techniques. Infrared studies show that the reaction produced acetaldehyde, acetic acid, acetate, formic acid, formate, and CO2/H2O. Modification of the Ti02 catalyst by Pt and Nafion slowed down the oxidation reaction through site blocking. Incorporation of Pt was found to favor formation of formate (HCOO ), indicating Pt decreases the rate of oxidation of formate more than that of its formation. [Pg.463]

Significant advances have been made in this decade in electrochemical H2 separation, mostly through the use of solid polymer electrolytes. Since the overpotentials for H2 reduction and oxidation are extremely low at properly constructed gas diffusion electrodes, very high current densities are achievable at low total polarization. Sedlak [13] plated thin layer of Pt directly on Nafion proton conductors 0.1-0.2cm in thickness, and obtained nearly 1200 mA/cm2 at less than 0.3 V. The... [Pg.208]

Yoon el al. [112] reported an all-solid-state sensor for blood analysis. The sensor consists of a set of ion-selective membranes for the measurement of H+, K+, Na+, Ca2+, and Cl. The metal electrodes were patterned on a ceramic substrate and covered with a layer of solvent-processible polyurethane (PU) membrane. However, the pH measurement was reported to suffer severe unstable drift due to the permeation of water vapor and carbon dioxide through the membrane to the membrane-electrode interface. For conducting polymer-modified electrodes, the adhesion of conducting polymer to the membrane has been improved by introducing an adhesion layer. For example, polypyrrole (PPy) to membrane adhesion is improved by using an adhesion layer, such as Nafion [60] or a composite of PPy and Nafion [117],... [Pg.304]

Direct-methanol fuel cells (DMFCs) have attracted considerable attention for certain mobile and portable applications, because of their high specific energy density, low poison emissions, easy fuel handling, and miniaturization [129,130], However, the methanol permeation through electrolyte membranes (usually called methanol cross-over) in DMFCs still is one of the critical problems hindering the commercialization [131,132], Nafion , a... [Pg.149]

For water electrolysis, GE used Nafion for the electrolyte as well as for a separator, mechanically pressing both electrodes against the membrane. Takenaka and Torikai proposed an electroless method for the deposition of noble metals on the surface of Nafion under wet conditions based on the difPiision of reducing agent through the membrane. ... [Pg.117]

To see the effects of methanol supplying method, methanol was supplied through the gas phase from the back (platinum) side of the SPE. When methanol is supplied through gas phase, methanol dissolves into Nafion and diffuses to the solution side eventually. Therefore, the measurements were conducted quickly after the supplying of methanol began. [Pg.185]

It is well known that Nafion ionomer contains both hydrophobic and hydrophilic domains. The former domain can facilitate gas transport through permeation, and the latter can facilitate proton transfer in the CL. In this new design, the catalyst loading can be further reduced to 0.04 mg/cm in an MEA [10,11]. However, an extra hydrophobic support layer is required. This thin, microporous GDL facilitates gas transport to the CL and prevents catalyst ink bleed into the GDL during applications. It contains both carbon and PTFE and functions as an electron conductor, a heat exchanger, a water removal wick, and a CL support. [Pg.65]

Because the reaction in a CL requires three-phase boundaries (or interfaces) among Nafion (for proton transfer), platinum (for catalysis), and carbon (for electron transfer), as well as reacfanf, an optimized CL structure should balance electrochemical activity, gas transport capability, and effective wafer management. These goals are achieved through modeling simulations and experimental investigations, as well as the interplay between modeling and experimental validation. [Pg.92]

How to balance Nafion ionomer contenf and Pf/C loading is a challenge for optimizing CL performance, due to fhe complexity induced by proton and electron conduction, reactant and product mass transport, as well as electrochemical reactions within the CL. The optimization of such a complex system is mainly implemented through multiple components and scale modeling, in combination with experimental validation. [Pg.92]

In the case of PEMs, the situation is more complicated because the sulfonate counter-ions (in the case of a PEM such as Nafion ) are bound to the polymer chain and are thus relatively immobile, in contrast to the free counter-ion in a small molecule acid such as sulfuric or acetic acid. Tethering of the sulfonate group can be considered to be an impediment to the mobility of the proton as it traverses the membrane. Proton mobility is also affected by the effective mean-free path of connectivity of the conduction pathway as shown in Figure 3.2. In situation (a), the increased number of dead ends and tortuosity of the aqueous domains through which proton transport occurs over the situation in (b) leads to lower overall mobility. This has been demonstrated by Kreuer and will be discussed later in this section. [Pg.109]

Based on GebeTs calculations for Nafion (where lEC = 0.91 meq/g),i isolated spheres of ionic clusters in the dry state have diameters of 15 A and an intercluster spacing of 27 A. Because the spheres are isolated, proton transport through the membrane is severely impeded and thus low levels of conductivity are observed for a dry membrane. As water content increases, the isolated ionic clusters begin to swell until, at X, > 0.2, the percolation threshold is reached. This significant point represents the point at which connections or channels are now formed between the previously isolated ionic clusters and leads to a concomitant sharp increase in the observed level of proton conductivity. [Pg.115]

Ren, X., Springer, T. E., Zawodzinski, T. A. and Gottesfeld, S. 2000. Methanol transport through Nafion membranes— Electro-osmotic drag effects on potential step measurements. Journal of the Electrochemical Society 147 466-474. [Pg.173]

Barragan, V. M., Ruiz-Bauza, C., Villaluenga, J. P. G. and Seoane, B. 2004. Transport of methanol and water through Nafion membranes. Journal of Power Sources 130 22-29. [Pg.173]

For the DMFC, Zhang et al. [127] used the sessile drop method to study the wettabilities of liquid methanol solutions on the surface of the anode DLs and MPLs. They were able to observe that the contact angles of the materials were the smallest with low PTFE content. In addition, the effect of Nafion ionomer content on the MPL (to increase hydrophilicity see Section 4.3.2) was also shown through the contact angle measurements (i.e., smaller contact angles compared to MPLs with PTFE). [Pg.251]

The reduction of the long-range diffusivity, Di by a factor of four with respect to bulk water can be attributed to the random morphology of the nanoporous network (i.e., effects of connectivity and tortuosity of nanopores). For comparison, the water self-diffusion coefficient in Nafion measured by PFG-NMR is = 0.58 x 10 cm s at T = 15. Notice that PFG-NMR probes mobilities over length scales > 0.1 /rm. Comparison of QENS and PFG-NMR studies thus reveals that the local mobility of water in Nafion is almost bulk-like within the confined domains at the nanometer scale and that the effective water diffusivity decreases due to the channeling of water molecules through the network of randomly interconnected and tortuous water-filled domains. ... [Pg.358]

Evaluation of Nafion Morphology through 4545 Studies of Oriented Membranes... [Pg.296]


See other pages where Nafion through is mentioned: [Pg.297]    [Pg.236]    [Pg.414]    [Pg.257]    [Pg.297]    [Pg.236]    [Pg.414]    [Pg.257]    [Pg.214]    [Pg.578]    [Pg.124]    [Pg.456]    [Pg.99]    [Pg.608]    [Pg.126]    [Pg.416]    [Pg.603]    [Pg.119]    [Pg.594]    [Pg.403]    [Pg.372]    [Pg.499]    [Pg.102]    [Pg.197]    [Pg.150]    [Pg.70]    [Pg.73]    [Pg.115]    [Pg.118]    [Pg.134]    [Pg.179]    [Pg.197]    [Pg.2]    [Pg.216]    [Pg.298]    [Pg.299]   
See also in sourсe #XX -- [ Pg.138 , Pg.139 , Pg.140 , Pg.141 , Pg.142 ]




SEARCH



Sodium transport through Nafion

Transport through Nafion

© 2024 chempedia.info